Calpain-mediated AQP2 proteolysis in inner medullary collecting duct
| Autor: | Donald T. Ward, Timothy G. Hammond, H. William Harris, Michelle A. Baum, Dechu P Puliyanda |
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| Rok vydání: | 2003 |
| Předmět: |
Male
medicine.medical_specialty Leupeptins Endosome Proteolysis Immunoblotting Biophysics Down-Regulation Endosomes Cysteine Proteinase Inhibitors Aquaporins urologic and male genital diseases Biochemistry Rats Sprague-Dawley chemistry.chemical_compound Internal medicine medicine Animals Trypsin Kidney Tubules Collecting Molecular Biology Calpastatin Aquaporin 2 Dose-Response Relationship Drug biology medicine.diagnostic_test Calpain urogenital system Calcium-Binding Proteins Leupeptin Caseins Dextrans Cell Biology Flow Cytometry Immunohistochemistry Aquaporin 6 Rats Cell biology Endocrinology chemistry biology.protein Dihydrotachysterol Calcium Protein Binding medicine.drug |
| Zdroj: | Biochemical and Biophysical Research Communications. 303:52-58 |
| ISSN: | 0006-291X |
| Popis: | Vitamin D-elicited hypercalcemia/hypercalciuria is associated with polyuria in humans and in animal models. In rats, dihydrotachysterol (DHT) induces AQP2 water channel downregulation despite unaltered AQP2 mRNA expression and thus we investigated the mechanism of AQP2 degradation. Incubation of AQP2-containing inner medullary collecting duct (IMCD) endosomes with Ca(2+) or calpain elicited AQP2 proteolysis, an effect abolished by leupeptin. This endogenous, Ca(2+)-sensitive protease activity exhibited a different proteolytic digest pattern from trypsin, which also degraded AQP2 in vitro. IMCDs contain abundant micro-calpain protein and functional calpain proteolytic activity as demonstrated by immunohistochemistry, immunoblotting, and gel zymography. Furthermore, by small particle flow cytometry we demonstrated that micro-calpain colocalizes with apical IMCD endosomes. DHT does not appear to elicit general proteolysis, however, in addition to AQP2 degradation, DHT treatment also diminished micro-calpain and calpastatin expression although whether these changes contributed to the AQP2 instability remains unclear. Together, these data show for the first time that AQP2 is a substrate for calpain-mediated proteolysis and that furthermore, micro-calpain, like AQP2, is both highly expressed in renal inner medulla and localized to apical IMCD endosomes. |
| Databáze: | OpenAIRE |
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